The present invention relates to the use of electronic systems in a well. More particularly, the present invention relates to a system for extending the life span and reliability of downhole electronic systems in a well, and for monitoring the operation of such electronic systems.
The development of hydrocarbon producing wells requires the installation of well completion equipment to monitor and control fluid flow. The characteristics of the well are monitored by the completion equipment and are transmitted to the surface. The transmitted data is analyzed by a reservoir management system, and completion equipment such as valves, sliding sleeves, packers and other completion tools are operated to control the well.
Electronic systems have been incorporated into well completion equipment. However, electronic systems downhole in a well may not adequately perform over the producing life of a well. If an electronic system should fail, reservoir management data and completion control operations would be interrupted until the equipment is repaired. This failure would interrupt well operations and would increase production costs.
High downhole temperatures in wells substantially reduce the life span of electronics in downhole equipment. Downhole well temperatures can exceed 150 degrees Centigrade, and such temperatures accelerate the corrosion mechanisms affecting electronic systems. Such corrosion mechanisms are accelerated by the presence of oxygen and water vapor in contact with metal components within the electronic systems.
Efforts have been made to mitigate the limitations presented by electronic systems downhole in wells. For example, one system uses fiber optics to operate a downhole pressure gauge system. The gauge senses downhole pressure changes through a response created by changes in the refractive index of a material caused by pressure fluctuations. The change in response is measured at the surface by monitoring changes in the optical signal transmitted from the surface to the downhole gauge and returned to the surface through a fiber optic cable.
Although optical systems may be useful with certain gauges, optical systems are limited because many well conditions and characteristics do not provide a direct optical response. Optical systems are also limited by the amount of power that can be transmitted by an fiber optic cable. Consequently, optical systems cannot perform the same functions provided by electronic systems for the processing of information or regulation of power.
Modern electronic systems are manufactured from a variety of metal alloys and other materials. Such alloys furnish key components for the functionality of the electronic systems, and include solders, metalized portions of the integrated circuits, etched copper alloys of printed circuit boards, and other metalizations used in the construction of printed circuit boards. These materials and compositions deteriorate with time and elevated temperatures.
Insulating flasks have been used in well logging tools to shield electronic components from high well temperatures. Dewar flasks have been used to insulate electronic logging components as the well logging tool is run in a well. While Dewar flasks successfully insulate downhole components for a limited time, the interior flask temperature eventually equalizes with the ambient well temperature and the thermal protection is lost.
Improvements to Dewar flask technology have been proposed to protect downhole electronic. U.S. Pat. No. 3,265,893 to Rabson et al. (1966) described a well logging tool having a thermally conductive heat sink for stabilizing the temperature in the logging tool for up to twenty hours. U.S. Pat. No. 4,671,349 to Wolk (1987) described a heat transfer wick for cooling the components of a well logging instrument for up to six hours during the interval of greatest heat exposure, and U.S. Pat. No. 3,488,970 to Hallenburg (1970) disclosed a module for cooling a water reservoir so that the cooled water could be pumped to transfer heat from the logging tool housing.
None of these techniques propose a system for protecting downhole electronic components over long time periods. Moreover, none of these systems propose a solution for monitoring the deterioration of electronic components within a downhole well tool. Accordingly, there is a need for a system that can perform these functions over the life of the well.